Background arts will be described in reference to FIGS. 5 to 6B. As illustrated in FIGS. 5 to 6B, a solenoid valve obtained by coupling together a linear solenoid 104 in which an outer opening 105a of a breathing passage 105 is located in a fitted part β′ between an outer connector 106 and a yoke 101; and a valve V′ (a spool valve in FIG. 5) driven by this linear solenoid 104, is known (see, for example, Japanese Patent No. 4569371 corresponding to US2006/0243938A1, and JP-A-2003-329164). In addition, Japanese Patent No. 4569371 describes the solenoid valve that uses a ring core 108 (magnetic material ring for delivering and receiving magnetism between a sliding core 112b and a cup bottom part of the yoke 101), and JP-A-2003-329164 describes the solenoid valve without using the ring core 108.
As described above, in the solenoid valve in which the outer opening 105a of the breathing passage 105 is located at a bottom part of the outer connector 106, when the outer connector 106 is disposed toward an upper portion of the yoke 101 (upper side in the vertical direction), the outer opening 105a opens on the upper side of the yoke 101. For this reason, a foreign substance falling from above (such as the case of an oil droplet falling from a mechanical part of an automatic transmission as illustrated on a right-hand side in FIG. 6B), or a foreign substance slowly falling in oil (such as the case of the valve being disposed in oil inside an oil pan as illustrated on a left-hand side in FIG. 6B) can easily enter into the breathing passage 105 through the outer opening 105a. 
The breathing passage 105 described in Japanese Patent No. 4569371 and JP-A-2003-329164 communicates between the fitted part β′ between the outer connector 106 and the yoke 101 (bottom part of the outer connector 106), and a volume changing chamber α′ formed between a plunger 103 and the bottom part of the yoke 101 by the shortest distance as illustrated in FIGS. 6A and 6B. Accordingly, when the outer connector 106 is arranged on the upper side, the foreign substance, which has entered into the breathing passage 105 through the outer opening 105a, easily reaches the volume changing chamber α′ (sliding part of the plunger 103). As a result, there is concern that a defect in sliding of the plunger 103 may be caused due to the foreign substance which has reached the volume changing chamber α′. Therefore, in the solenoid valve by the conventional technology, there has been concern that malfunctions may be caused as a result of entering of the foreign substance in the case of the outer connector 106 being disposed upward.